Triacylglycerides represent the major form of energy storage in eukaryotes, and disorders or imbalance in triacylglyceride metabolism are implicated in the pathogenesis and increased risk for obesity, insulin resistance, type II diabetes, nonalcoholic fatty liver disease and coronary heart disease (Lewis, et al., Endocrine Reviews 23:201, 2002). Storage of excess triacylglycerides in lean tissues, such as liver, muscle, and other peripheral tissues, leads to lipid-induced dysfunction in those tissues; thus, reducing fat accumulation in nonadipose sites appears to be of benefit in the treatment of lipotoxicity (Unger, R. H. Endocrinology, 144: 5159-5165, 2003). Accumulation of excess triacylglycerides in white adipose tissue (WAT) leads to obesity, a condition that is associated with decreased life span, type II diabetes, coronary artery disease, hypertension, stroke, and the development of some cancers (Grundy, S. M. Endocrine 13(2): 155-165, 2000). Obesity is a chronic disease that is highly prevalent in modern society and current pharmacological treatment options are limited, creating a need to develop pharmaceutical agents for the treatment of obesity that are safe and effective.
Diacylglycerol O-acyltransferases (DGATs) are membrane-bound enzymes that catalyze the terminal step of triacylglycerides biosynthesis. Two enzymes that display DGAT activity have been characterized: DGAT-1 (diacylglycerol O-acyltransferase type 1) (U.S. Pat. No. 6,100,077; Cases, et al., Proc. Nat. Acad. Sci. 95:13018-13023, 1998) and DGAT-2 (diacylglycerol O-acyltransferase type 2) (Cases, et al., J. Biol. Chem. 276:38870-38876, 2001). DGAT-1 and DGAT-2 share only 12% sequence identity. Significantly, DGAT-1 null mice are resistant to diet-induced obesity and have increased sensitivity to insulin and leptin (Smith, et al., Nature Genetics 25:87-90, 2000: Chen and Farese, Trends Cardiovasc Med. 10:188, 2000: Chen et al. J. Clin. Invest. 109:10049, 2002). DGAT-1 deficient mice are protected against hepatic steatosis, demonstrate increased energy expenditure, and decreased levels of tissue triacylglycerides. In addition to improved triacylglycerides metabolism, DGAT-1 deficient mice also have improved glucose metabolism, with lower glucose and insulin levels following a glucose load, in comparison to wild-type mice. Partial DGAT-1 deficiency in heterozygous DGAT-1+/−animals is sufficient to deliver an intermediate phenotype on body weight, adiposity, and insulin and glucose metabolism when compared to wild type and homozygous littermates (Chen and Farese, Arterioscler. Thromb. Vase. Biol. 25:482-486, 2005), and small molecule DGAT-1 inhibitors have been reported to induce weight loss in diet-induced obese (DIO) mice (US 2004/0224997). The phenotypes of DGAT-1 deficient mice, and the pharmacological activity reported with DGAT-1 inhibitors suggests that the discovery of small molecules that effectively block the conversion of diacylglycerol to triacylglycerides by inhibiting the DGAT-1 enzyme can have utility in the treatment of obesity and other diseases associated with triacylglycerides imbalance.